The polyamines, spermidine (spd) and spermine (sp), and the diamine, putrescine (pu) may be required to maintain the structure and/or function of nucleic acids; therefore, the control of their synthesis assumes great importance. Ornithine decarboxylase (ODC) (EC4.1.1.17; L-ornithine carboxy-lyase) is an important control point for polyamine biosynthesis through pu. The molecular events that control ODC are unclear, although available information suggests that the rate of synthesis and degradation are both altered. Among other things, pu and spd may inhibit translation of the ODC mRNA. The long term goals of the proposed project are to elucidate the mechanisms by which ODC is regulated in normal and cancer cells and to purify and characterize ODC from a simian adenovirus 7-induced hamster brain tumor (HaBT). Specifically, we propose to investigate: the ODC activity of high density, nongrowing HaBT cells in culture upon addition of various growth stimulants and inhibitors. We also propose to purify the ODC from HaBT cells grown in hamsters to obtain enzyme that can be used as an antigen in the development of a radioimmunoassay for the enzyme.